242 HETEROGENETIC ORIGIN 



growths, or in the substance of the thick pellicle itself, these 

 minute Amoeboid bodies appear in myriads and go on to the 

 production of Ciliate matrices such as we see in Figs. 49, 50, and 

 51 ; while in a weak or a shallow infusion, forming only a thin 

 pellicle, no such bodies present themselves. 



Then, again, in the cases where these minute Amoeboid bodies 

 arise and go on to the formation of Ciliate matrices, is it con- 

 ceivable that myriads of them, always of precisely the same kind, 

 should occur in each particular infusion if they were due to 

 external contamination ? It cannot be supposed that their vast 

 numbers are due to self- multiplication ; for such particles are 

 motionless, and through their various stages of growth can 

 never be seen to divide till they have attained their full size and 

 have become converted within their cysts into embryo Ciliates. 



There is the further important fact, telling strongly against 

 the origin either of the primary or of the secondary forms from 

 external contamination, that Ciliates only appear in filtered 

 infusions prepared from ripe or from dead grasses, and not 

 from immature grasses in the fresh state, as I have shown else- 

 where.' If contamination came from earth, or air, there seems 

 absolutely no reason why it should not come with fresh, immature 

 grasses, as well as from ripe, dead grasses. 



A striking illustration of this kind of difference has again been met with 

 quite recently. On June 14th I gathered some of the Common Holcus 

 [H. lanatus), which was just beginning to flower, cutting each stalk about 

 two inches from the ground. On reaching home, within an hour, I cut up some 

 of the stalks and leaves and made an infusion in the ordinary way, except that 

 I used distilled instead of tap water. After macerating for four hours at about 

 80° F. the infusion was filtered through two layers of fine Swedish paper, and 

 placed under a bell-jar. After three days the turbidity was only slight, and 

 the scum on the surface was scarcely appreciable : it was very thin and non- 

 coherent even on the fifth day, and showed, on examination, nothing but 

 Bacteria. The scum was examined again on the tenth and on the fourteenth 

 days, and was found on each occasion to be thin and to contain only different 

 kinds of Bacteria : not a single Zoogloea mass. Monad, Amoeba or Ciliate was 

 found on either occasion. 



On June 22nd another similar infusion was made with distilled water from 

 the stalks and leaves of some of the same grasses, which, during the intervening 

 eight days, had been lying on a newspaper within a closed drawer. Everything 

 was the same, therefore, except that the infusion was made from grasses which 

 instead of being fresh had been dead for eight days. The infusion was filtered 

 in the same way, and then placed beneath the bell-jar by the side of the 

 other. After thirty-six hours this second infusion was already much more 



' " Studies in Heterogenesis," p. 87. 



